Optimized plate fin heat exchanger for improved compliance to improve thermal life

ABSTRACT

A heat exchanger includes a hot passage; a cold passage adjacent the hot passage; a pair of tube sheets, with one tube sheet on each opposing side of one of the hot passage and the cold passage; a fin in one of the hot passage and the cold passage; wherein the fin includes a first distal portion, a second distal portion, and an intermediate portion between the first and second distal portions; wherein the fin is configured to provide, at only the first distal portion and the second distal portion, improved flexibility in three degrees of freedom of movement within one of the hot passage and the cold passage.

BACKGROUND OF THE INVENTION

The present invention generally relates to heat exchangers and, moreparticularly, apparatus and methods for minimizing strain in heatexchangers to achieve a longer useful life or enabling the heatexchanger to tolerate a more severe operating environment.

Plate-fin heat exchangers are brazed to form a core that is a monolithicstructure where the each tube sheet layer is locked into closesynchronicity with its two neighboring tube plate. Each of the internaltube sheets is connected to a neighboring tube sheet via the hot sidefins and to the other neighboring tube sheet via the cold side fins.With this rigid, non-compliant construction, heat exchangers can exhibita significant strain when the heat exchanger has a temperaturedifference placed on the unit, especially when the operationallytemperature difference is large. This strain can lead to conditionswhere, with repeated exposure, the tube sheet cracks, thus negativelyimpacting the performance of the system and the useful life of the heatexchanger. A typical situation where this issue may occur is with bleedair pre-coolers that are found on most commercial (large and small) andmilitary environmental control/bleed air systems. Any heat exchangerthat is repeatedly exposed to rapid and large temperature differencesmay exhibit this issue.

As can be seen, there is a need for improved apparatus and methods forreducing strain in heat exchangers.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a heat exchanger comprises a hotpassage; a cold passage adjacent the hot passage; a pair of tube sheets,with one tube sheet on each opposing side of one of the hot passage andthe cold passage; a fin in one of the hot passage and the cold passage;wherein the fin includes a first distal portion, a second distalportion, and an intermediate portion between the first and second distalportions; wherein the fin is configured to provide, at only the firstdistal portion and the second distal portion, three degrees of freedomof movement within one of the hot passage and the cold passage.

In another aspect of the present invention, a plate fin heat exchangercomprises a hot passage; a cold passage adjacent the hot passage; a pairof tube sheets on opposing sides of the cold passage; a fin in the coldpassage; wherein the fin includes a first distal portion, a seconddistal portion, and an intermediate portion between the first and seconddistal portions; wherein the fin, at only the first distal portion andthe second distal portion, is separated laterally into a first lateralportion and a second lateral portion.

In a further aspect of the present invention, a plate fin heat exchangercomprises a plurality of cold passages; a plurality of fins in the coldpassages; a plurality of hot passages; a plurality of tube sheets;wherein the cold passages, hot passages and tube sheets are positionedin an recurring pattern of cold passage, tube sheet, hot passage, andtube sheet; wherein one of the plurality of fins has a distal portionwith a divided configuration to provide three degrees of freedom ofmovement of the fin at the distal portion.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a heat exchanger according to anembodiment of the present invention;

FIG. 2 is a close up view of a portion of the heat exchanger of FIG. 1;

FIG. 3 is a close up perspective view of a portion of a heat exchangeraccording to another embodiment of the present invention;

FIG. 4 is a plan view of a portion of a heat exchanger according to afurther embodiment of the present invention;

FIGS. 5A-5B are schematic top views of a heat exchanger depicting twovariations of compliant fin separation according to embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out exemplary embodiments of the invention. Thedescription is not to be taken in a limiting sense, but is made merelyfor the purpose of illustrating the general principles of the invention,since the scope of the invention is best defined by the appended claims.

Various inventive features are described below that can each be usedindependently of one another or in combination with other features.

Broadly, embodiments of the present invention generally provides a heatexchanger that can minimize the locking of a tube sheet to its twoneighboring tube sheets. In embodiments, the heat exchanger can includea hot circuit usually at high pressure and a cold circuit at relativelylow pressure. This is the case for bleed air pre-coolers found oncommercial and military aircraft. Tube sheets that surround a hotpassage can be brazed to the hot side fin to provide for pressurecontainment of the high pressure fluid. However, the tube sheets thatsurround the cold side passage are not connected or otherwise affixed,in certain locations, to one another. This is possible due to the lowpressure of the fluid in this passage.

FIG. 1 depicts a heat exchanger 10 according to an embodiment of thepresent invention. The heat exchanger 10 can be of a plate finconstruction and receive, at a cold inlet face 17, a cold flow 11, suchas a fan air flow in the context of an aircraft, and which exits at acold outlet face (not shown). The heat exchanger 10 can also receive, ata hot inlet face 18, a hot flow 12, such as a bleed air flow in thecontext of an aircraft, and which exits at a hot outlet face (notshown).

A core of the heat exchanger 10 can include a plurality of cold passages13 that can receive the cold flow 11 at the cold inlet face 17 of theheat exchanger 10. The cold passages 13 can include a plurality of mainor primary cold passages 13 a that may be generally located in a centerarea of the core. The cold passages 13 can further include outer ordistal cold passages 13 b at one side of the main cold passages 13 a, inaddition to outer or distal cold passages 13 c at an opposite side ofthe main cold passages 13 a. The outer passages 13 b, 13 c can be at thefar ends/side areas of the core.

The outer cold passages 13 b can include a distal portion or area 13 b-1and a distal portion or area 13 b-2 at opposed corners of the heatexchanger 10 where the cold passages 13 meet hot passages 14 asdescribed below. Between the distal portions 13 b-1, 13 b-2 can be anintermediate portion 13 b-5. Similarly, the outer cold passages 13 c caninclude a distal portion or area 13 c-1 and a distal portion or area 13c-2 at opposed corners of the heat exchanger 10 where the cold passages13 meet the hot passages 14. Between the distal portions 13 c-1, 13 c-2can be an intermediate portion 13 c-5.

FIG. 2 is a close up view of the distal portion or area 13 b-2 of thecold passages 13. The distal portion 13 b-2 can be defined by an areahaving a length 13 b-3 and a height 13 b-4. The other distal portions 13b-1, 13 c-1, and 13 c-2 can be similarly defined, and the widths andlengths can be different or the same from one another and with differentdetailed modification of the fin geometry.

In embodiments of the distal portion 13 b-2, the height 13 b-4 can bemeasured in numbers of cold passages 13 b. For example, the number ofcold passages 13 b in height 13 b-4 can be from about 4 to about 8passages specifically and from 2 to 10 as a general range, as anexample. The number of passages that form the passages 13 b can dependon the thermal stresses that are induced upon the core with theoperational conditions.

In embodiments of the distal portion 13 b-2, the ratio of the length 13b-3 to the height 13 b-4 may be from about 0.5 to about 1.0 specificallyand from 0.2 to 2.0 as a general range.

In embodiments, the length 13 b-3 may be from about 0.5 to about 1.5inches specifically and from 0.2 to 2 inches as a general range.

In embodiments, the ratio of the height 13 b-4 to the overall height ofthe cold inlet face may be from about 5% to about 10% specifically andfrom 3% to 18% as a general range, though this number is dependent uponthe cold inlet face width which can vary greatly for the heat exchanger.

The foregoing ratios may be the same or different among the other distalportions 13 b-1, 13 c-1, and 13 c-2.

Referring back to FIG. 1, the core of the heat exchanger 10 canadditionally include a plurality of hot passages 14 that can receive thehot flow 12 at the hot inlet face 18 of the heat exchanger 10. The hotpassages 14 can include a plurality of main or intermediate hot passages14 a. The hot passages 14 can further include outer or distal hotpassages 14 b at one side of the main hot passages 14 a, in addition toouter or distal hot passages 14 c at an opposite side of the main hotpassages 14 a.

Further, the core of the heat exchanger 10 can include a plurality oftube sheets 15 that, in an embodiment, can form a recurring pattern ofcold passage 13, tube sheet 15, hot passage 14, and tube sheet 15 (FIG.2). Therefore, any one tube sheet (such as tube sheet 15-1) has twoimmediately adjacent or neighboring tube sheets (such as tube sheets15-2, 15-3). And, one tube sheet can be on each of the opposed sides ofthe any one tube sheet.

In the core of the heat exchanger 10, a fin may be disposed in one ormore cold passages 13. Differently configured fins may be disposed indifferent cold passages 13. In an embodiment, a fin 17 having a main orbase configuration can be disposed in one or more of the main coldpassages 13 a. In an embodiment, a fin 16 having an outer or dualconfiguration can be disposed in one or more of the outer cold passages13 b, 13 c.

For example, the fin 17 may have a wave or sinusoidal configuration overits entire cross section—from a first distal portion at a first end ofthe fin 17 and to a second distal portion at a second send of the fin 17(FIG. 2). In other words, the fin may have such configuration from thecold inlet face 17 to a cold outlet face (not shown) where the cold flowexits, and also have such configuration from the hot inlet face 18 to ahot outlet face (not shown) where the hot flow exits.

In contrast, and as an example, the fin 16 may have a wave or sinusoidalconfiguration 16 c but only over its cross section in the intermediateportion (e.g., 13 b-5). At one or both of its first and second distalportions, respectively located at its first and second distal ends, thefin 16 may have a divided wave or sinusoidal configuration. In otherwords, the fin may be separated laterally through its cross section atone or both of its distal portions or ends, but not in its intermediateportion. Thereby, the fin 16, at one or both of its distal portions/endscan have a first lateral portion 16 a and a second lateral portion 16 b(FIGS. 2-3).

In embodiments, the fin may be laterally separated at itscross-sectional mid-point (FIGS. 2-3) or at other points along the fin.In embodiments, the lateral separation may be less (FIG. 5A) than theentire distance (FIG. 5B) between the cold inlet face and the coldoutlet face, and it may be in multiple segments between the cold inletface and the cold outlet face. In embodiments, the distal portions ofthe fin 16 may or may not have the same lateral separation, if any atall.

As depicted in FIG. 3, with the first lateral portion 16 a separatedfrom the second lateral portion 16 b, such first and second lateralportions can have three degrees of freedom of movement withoutconfinement from attachment to neighboring fins, i.e., movement in an x,y, and z direction. In embodiments, the three degrees of freedom ofmovement may be increased over the movement that may already exist. Forexample, in the “x” direction, the movement may be increased by about0.1% to about 2%. In the “y” direction, the movement may be increased byabout 2% to about 20%. In the “z” direction, the movement may beincreased by about 0.1% to about 2%.

FIG. 4 is an alternative embodiment of the first and second lateralportions, but in the context of distal portion 13 b-1′ which correlatesto 13 b-1 in FIG. 2. This embodiment is otherwise the same as theembodiment depicted in FIG. 2. This embodiment could be applied to 13b-2, 13 c-1 or 13 c-2. In FIG. 4, a fin 16′ includes an intermediateportion 16 c′ which is generally of a wave or sinusoidal configuration(or could be in other configurations, such as plain or offset fin). Afirst lateral portion 16 a′ and a second lateral portion 16 b′ are twowave or sinusoidal configurations (whereas 16 a and 16 b of FIG. 2 areportions of a single wave or sinusoidal configuration). In other words,the lateral portion 16 a′ is a wave or sinusoidal configuration stackedon the lateral portion 16 b′ which is a separate wave or sinusoidalconfiguration.

In yet another embodiment, a splitter plate may be disposed laterallythrough a fin, keeping fin 16 a′ and 16 b′ separated. To relieve stress,portions of the fin at its distal ends may be unbrazed to the fins orotherwise disconnected from the plate. Or, the plate may be eliminatedat the distal ends of the fin.

If the disconnection of the complete cold side fin causes other issues(such as pressure containment), the fins could be modified in selectlocations such as near the hot-hot, hot-cold and cold-hot corners, for−2 inches into the core and −2 inches away from the bar (FIG. 5A). It ispossible the amount/area of disconnection would vary depending on whatcorner is being modified.

For embodiments, preliminary structural analysis and investigation ofstrain range reduction associated with this invention is 17% on atypical commercial transport pre-cooler for the worst transient maneuverif applied to the whole heat exchanger. The strain reduction is 8% ifthe cold side fin cut were applied only to the top and bottom six coldside passages with the passages in the center of the core unmodified.This is a significant strain decrease and would result in a much moreincrease in estimated pre-cooler useful life than the 17% due to theassociated strain reduction. This analysis is preliminary in nature andwas conducted without reflecting the reduction in the stackwiseconduction due to the fin cut at the mid-plane. The structural analysiswas conducted with a complete disconnection of the fins in the threedirections at the mid-plane.

It should be understood, of course, that the foregoing relates toexemplary embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

We claim:
 1. A heat exchanger, comprising a hot passage; a cold passageadjacent the hot passage; a pair of tube sheets, with one tube sheet oneach opposing side of one of the hot passage and the cold passage; a finin one of the hot passage and the cold passage; wherein the fin includesa first distal portion, a second distal portion, and an intermediateportion between the first and second distal portions; wherein the fin isconfigured to provide, at only the first distal portion and the seconddistal portion, three degrees of freedom of movement within one of thehot passage and the cold passage.
 2. The heat exchanger of claim 1,further comprising a plurality of tube sheets, whereby any one tubesheet has two immediately adjacent tube sheets, whereby one tube sheetof the two immediately adjacent tube sheets is on each side of the anyone tube sheet.
 3. The heat exchanger of claim 1, wherein the pair oftube sheets are on opposing sides of the cold passage, and the pair oftube sheets are not affixed to one another at certain locations.
 4. Theheat exchanger of claim 1, wherein the fin has a sinusoidalconfiguration.
 5. The heat exchanger of claim 1, wherein one of thefirst distal portion and the second distal portion has a dividedsinusoidal configuration.
 6. The heat exchanger of claim 1, wherein oneof the first distal portion and the second distal portion is separatedlaterally through its cross section.
 7. The heat exchanger of claim 1,wherein the fin is laterally separated at its cross-sectional mid-point.8. A plate fin heat exchanger, comprising a hot passage; a cold passageadjacent the hot passage; a pair of tube sheets on opposing sides of thecold passage; a fin in the cold passage; wherein the fin includes afirst distal portion, a second distal portion, and an intermediateportion between the first and second distal portions; wherein the fin,at only the first distal portion and the second distal portion, isseparated laterally into a first lateral portion and a second lateralportion.
 9. The heat exchanger of claim 8, further comprising: aplurality of cold passages, wherein the plurality of cold passagesinclude outer cold passages, and wherein the cold passage with the fintherein is one of the outer cold passages.
 10. The heat exchanger ofclaim 9, wherein the plurality of outer cold passages includes a distalarea defined by an area having a length and height.
 11. The heatexchanger of claim 10, wherein a ratio of the length to the height isfrom about 0.5 to about 1.0.
 12. The heat exchanger of claim 10, furthercomprising a cold inlet face, and wherein a ratio of the height of thedistal area to an overall height of the cold inlet face is from about 3%to about 11%.
 13. The heat exchanger of claim 9, wherein the pluralityof outer cold passages includes from about 4 to about 8 cold passages.14. The heat exchanger of claim 8, wherein: the cold passage includes acold passage distal portion located at a corner where the cold passagemeets the hot passage, and one of the first and second distal portionsof the fin is located at the cold passage distal portion.
 15. A platefin heat exchanger, comprising a plurality of cold passages; a pluralityof fins in the cold passages; a plurality of hot passages; a pluralityof tube sheets; wherein the cold passages, hot passages and tube sheetsare positioned in an recurring pattern of cold passage, tube sheet, hotpassage, and tube sheet; wherein one of the plurality of fins has adistal portion with a divided configuration to provide three degrees offreedom of movement of the fin at the distal portion.
 16. The heatexchanger of claim 15, wherein the divided configuration is a lateralseparation through a cross section of the distal portion.
 17. The heatexchanger of claim 16, wherein the lateral separation is at a mid-pointof the cross section.
 18. The heat exchanger of claim 16, wherein thelateral separation is less than an entire distance between a cold inletface and a cold outlet face.